The present invention relates to a process for producing a polyarylene sulfide (hereinafter simply referred as PAS) and, particularly, the present invention relates to a novel process for producing a high-molecular-weight or ultra-high-molecular-weight granular PAS of an excellent handling property at an inexpensive cost without using a polymerization aid such as an organic acid salt, and a high-molecular-weight or ultra-high-molecular-weight granular PAS of an excellent handling property produced by the process thereof. More in detail, the present invention relates to a process for producing a high-molecular-weight or ultra-high-molecular-weight granular PAS of an excellent handling property, which the process comprises:
(1) a preliminary polymerization step of subjecting an alkali metal sulfide and a dihalo aromatic compound to dehalogenation and sulfidation in such a system that the amount of an aprotic organic polar solvent used is from 0.2 to 5 kg per one mol of the alkali metal sulfide charged and from 0.5 to 5 mol of water is present together per 1 kg of the organic polar solvent, until the conversion of the charged dihalo aromatic compound reaches from 50 to 98 mol % and the melt viscosity of the resultant PAS prepolymer reaches 5 to 300 poise (as measured at 310.degree. C. under a shear rate of 200 sec.sup.-1), and
(2) a two-phase separated polymerization step of adding water to the resultant reaction mixture such that from 5.5 to 15 mol of water is present per 1 kg of the organic polar solvent in the reaction system without separating the resultant prepolymer from the reaction system,
(i) heating and maintaining the reaction system at a temperature of about 257.degree. to about 290.degree. C. for at least 10 minutes while stirring,
(ii) lowering the temperature of the reaction system and maintaining the reaction system at a temperature of about 220.degree. to about 250.degree. C. for at least 2.0 hours while stirring, and
(iii) if necessary, heating and maintaining the reaction system at a temperature of about 250.degree. to about 290.degree. C. for a sufficient time to form a polyarylene sulfide of a desired melt viscosity while stirring, and the present invention also relates to a process for producing a high-molecular-weight or ultra-high-molecular-weight granular PAS of an excellent handling property, which the process comprises:
(1) a preliminary polymerization step of subjecting an alkali metal sulfide and a dihalo aromatic compound to dehalogenation and sulfidation in an aprotic organic polar solvent, thereby forming a PAS prepolymer having a melt viscosity from 5 to 300 poise (as measured at 310.degree. C. under a shear rate of 200 sec.sup.-1), and
(2) a two-phase separated polymerization step of separating the resultant PAS prepolymer, dispersing the thus separated prepolymer in an aprotic organic polar solvent containing from 5.5 to 15 mol of water per 1 kg of the organic polar solvent such that from 0.5 to 3.5 mol of the arylene group in the prepolymer is present per 1 kg of the organic polar solvent,
(i) heating the thus obtained dispersion in a strongly alkaline condition (pH of the 10-fold diluted dispersion with water is not less than 9.5) and maintaining the reaction system at a temperature of about 257.degree. to about 290.degree. C. for at least 10 minutes while stirring,
(ii) lowering the temperature of the reaction system and maintaining the reaction system at a temperature of about 220.degree. to about 250.degree. C. for at least 2.0 hours while stirring, and
(iii) if necessary, heating and maintaining the reaction system at a temperature of about 250.degree. to about 290.degree. C. for a sufficient time to form a polyarylene sulfide of a desired melt viscosity while stirring, and a high-molecular-weight or ultra-high-molecular-weight granular PAS of an excellent handling property produced by the above-mentioned process.
The terms "high-molecular-weight PAS" and "ultra-high-molecular-weight PAS" used in the present invention indicate respectively those PASs having a melt viscosity of from about 1000 to about 7000 poise and more than about 7000 poise (as measured at 310.degree. C. under a shear rate of 200 sec.sup.-1).
In recent years, thermoplastic resins of higher heat-resistance have been increasingly demanded as a material for the production of electronic equipments and automobile parts.
While PAS has properties capable of satisfying these requirements, it is usually rather difficult to obtain PAS typically represented by polyphenylene sulfide of sufficiently high molecular weight. Therefore, there has been a problem that it is very difficult to obtain fibers or films requiring high strength and molded products requiring high impact strength.
The present invention intends to provide a process for producing a PAS of remarkably high-molecular-weight at an inexpensive cost for solving these problems.
As a typical process for the production of PAS, a process of reacting a dihalo aromatic compound and sodium sulfide in an organic amide solvent such as N-methylpyrrolidone has been disclosed in Japanese Patent Publication No. 45-3368 (U.S. Pat. No. 3,354,129). However, PAS produced by this proposed method is of a low molecular weight and low melt viscosity, and it is difficult to mold it into molded articles, films, sheets, fiber, etc.
In view of the above situation, various methods of improving the process for producing high-molecular-weight PAS have been proposed.
Among the improved methods, a most typical method as described in Japanese Patent Publication No. 52-12240 (U.S. Pat. No. 3,919,177) uses an alkali metal organic acid salt as a polymerization aid in the reaction between a dihalo aromatic compound and sodium sulfide in an organic amide solvent such as N-methyl pyrrolidone. According to this method, the polymerization aid has to be added approximately in an equimolar amount to the alkali metal sulfide and, further, it is required to use a large amount of lithium acetate or sodium benzoate which is expensive in order to obtain particularly a PAS of rather high polymerization degree, and accordingly the production cost of PAS is increased, resulting in an industrial disadvantage.
Further, according to this method, a large amount of organic acid, etc. are liable to contaminate waste water upon recovery of PAS after the polymerization reaction, thereby possibly causing a problem in view of public pollution in this method and there are serious problems from the economical point of view such as requirement of enormous facilities and much running cost for the recovery, reuse and waste of the polymerization aid for prevention of such problems.
As another method of producing PAS of high polymerization degree, there has been proposed a method of using a tri- or higher polyhalo aromatic compound as a crosslinking agent or branching agent during polymerization or at the terminal stage of polymerization [Japanese Patent Application Laid Open (KOKAI) No. 53-136100 (U.S. Pat. No. 4,116,947) etc.].
Although a high-molecular-weight PAS having apparent melt viscosity of several tens of thousands poise can be obtained easily, according to this method of increasing the polymerization degree only by means of the crosslinking agent, this PAS is a highly crosslinked or branched polymer, so that it is poor in the spinnability property and difficult to mold into films or fibers. Further, even if molded articles happen to be obtained, they are mechanically extreme since the molecular chain is basically short.
In view of the foregoing problems, the present inventors have made an intensive study on the polymerization mechanism of the alkali metal sulfide and dihalo aromatic compound in a simple polymerization system in order to find a process for producing a linear PAS having a sufficiently high melt viscosity at a reduced cost without using a polymerization aid such as an alkali metal organic acid salt, and as a result, it has been found that PAS of remarkably high molecular weight can be produced without using any polymerization aid by making a significant difference in various polymerization conditions, particularly, the amount of coexistent water and the polymerization temperature between 1st polymerization step (preliminary polymerization step) and 2nd polymerization step (two-phase separated polymerization step [Japanese Patent Application Laid-Open (KOKAI) No. 61-7332 (U.S. Pat. No. 4,645,826)].
Then, the present inventors have found a process for producing high to ultra-high-molecular-weight PAS by once separating and dispersing the prepolymer in a water-containing polar solvent and then heating the resultant dispersion [Japanese Patent Application Laid-Open (KOKAI) No. 61-66720 (U.S. Pat. No. 4,645,826)].
Any of the methods as described above, developed by the present inventors can be said as a process for producing a high- or ultra-high-molecular-weight PAS by using a watercontaining organic polar solvent as a solvent, thereby causing liquid/liquid two-phase separation (dispersion phase: a liquid phase rich in polymer, and continuous phase: a liquid phase poor in polymer), that is, so to speak "two-phase separated polymerization".
In the two-phase separated polymerization process, it is possible, in a laboratory scale, to prepare an ultra-high-molecular-weight PAS or a PAS by a high polymer-concentration-recipe. However, in the case of industrially producing a PAS in a commercial plant, the dispersion phase reaches a so-called "sticky state" during polymerization, in which the dispersion phase droplets are amalgamated by mutual collision, grown to coarse particles and eventually to lumps. Therefore, the agitation of the stirrers and the discharge of the polymer from the reactors become difficult. Accordingly, there has left a problem, from a technological point of view, for industrially producing an ultra-high-molecular-weight PAS or a PAS by a high polymer-concentration recipe.
Both of the method as described in Japanese Patent Application Laid Open (KOKAI) No. 61-7332 (U.S. Pat. No. 4,645,826) and the method of Japanese Patent Application Laid Open (KOKAI) No. 61-66720 (U.S. Pat. No. 4,645,826) may be called a "two-phase separated polymerization" for producing a high-molecular-weight or ultra-high-molecular-weight linear PAS at an inexpensive cost with no substantial use of the crosslinking agent or polymerization aid (organic acid salt, etc.), and each of them comprises a process of at first preparing a prepolymer of a melt viscosity from 5 to 3000 poise (as measured at 310.degree. C. under a shear rate of 200 sec.sup.-1), heating the resultant prepolymer to about 240.degree. to 290.degree. C. in a strongly alkaline water-containing aprotic organic polar solvent containing a sufficient amount of water, and carrying out a liquid-liquid two-phase separated polymerization (dispersion phase: a liquid phase rich in polymer, and continuous phase: a liquid phase poor in polymer), thereby obtaining a polyarylene sulfide of higher molecular weight.
As the two-phase separated polymerization proceeds in this process, the dispersion phase is thought to become more viscous gradually and to reach within the region of the so-called "sticky state" where dispersion phase droplets are liable to be amalgamated and hard to be devided (the region is particularly wide in a high polymer-concentration recipe.)
Then, the dispersion phase droplets are amalgamated by mutual collision, grown to coarse particles and eventually to lumps.
The present inventors have made an intensive study on the method as described above for preventing the dispersion phase from forming the sticky state during polymerization and preventing the dispersion phase droplets from amalgamation or growing. Then it has been found that by conducting the two-phase separated polymerization in the reaction system containing the polyarylene prepolymer and from 5.5 to 15 mol of water per 1 kg of an organic polar solvent by way of the following procedures:
(i) heating and maintaining the reaction system at a temperature of from about 257.degree. to about 290.degree. C. with stirring in order to form a liquid-liquid-two-phase and to proceed polymerization,
(ii) lowering the temperature of the reaction system before the dispersion phase becomes viscous and forms a sticky state, and stirring the reaction system at a temperature of from about 220.degree. to about 250.degree. C. for at least 2.0 hours, and
(iii) heating the reaction system, if necessary, to a temperature of from about 250.degree. to about 290.degree. C. for a sufficient time to form a polyarylene sulfide of a desired melt viscosity with stirring, while the dispersion phase droplets prevented from amalgamation or growing and an ultra-high-molecular-weight granular PAS or high-molecular-weight granular PAS of an excellent handling property has been obtained, and based on the findings as described above, the present invention has been attained.